Harder KranK durometer bushings (96a & 93a) are for heavier-weight riders (over 175lbs) as harder durometer bushings allow for a nice tight set-up.
Medium KranK durometer bushings (90a & 87a) are best for medium-weight riders (125lbs & over) as well as for those looking for a looser setup in the RoadSide position when coupled with a harder duro bushing.
Softer KranK durometer bushings (84a) are best for lightweight riders (under 125lbs). Super fun for those looking for a really loose setup.
PLEASE NOTE: The KranK Formula has quite a bit of adjustability - so order accordingly! You can tighten the kingpin nut up to two full turns to 'harden' or 'loosen' the duro.